High-mode vortex-induced vibration and its mitigation of no-hanger main cable of the side span in a cable-stayed suspension bridge

In recent years, harmful vortex-induced vibrations of high-order modes of super long stay cables have been observed on several cable-stayed bridges with the main span near 1000 m. The possibility of high-mode vortex-induced vibrations of the no-hanger main cable of the side span of a cable-stayed suspension bridge was carefully investigated based on wind tunnel tests by using a three-dimensional elastic test model. First, the cable's three-dimensional elastic test model was designed and manufactured. Second, a series of wind tunnel tests were carried out to measure the no-hanger main cable's wind-induced responses. The results show that large-amplitude oscillation of the test model was observed under the wind angles of 0 & DEG;, & PLUSMN;50 & DEG; and +60 & DEG;, and the highest mode observed in the test is 16(th) order. The Strouhal number for & alpha; = 0 & DEG; is about 0.195, while the values for & alpha;= & PLUSMN;50 & DEG; are about 0.12. Third, the effects of structural damping and helical wire on the high-mode vortex-induced vibration of this main cable were studied in detail. The results show that the high-order vortex-induced vibration of the cable can be successfully mitigated by increasing the damping ratios up to 0.25% or by the helical wire with a pitch of 12D.